With development of the access network, different access technologies thrive, including ADSL2+ (Asymmetric Digital Subscriber Line, asymmetric digital subscriber line) and digital subscriber line (Digital Subscriber Line, shorted as DSL hereinafter) of VDSL2 (Very-high-bit-rate Digital Subscriber loop, very-high-bit-rate digital subscriber loop) that are considered as the most advanced and operable mainstream technologies. The DSL technology uses the existing entering-home copper strand wire as the medium and provides different bandwidth through different modulation modes to implement access of subscribers with different rates and solve the problem of last-mile access.
Copper cables for transmitting DSL signals are generally laid at an outdoor exposed environment at a length of several miles and are easy to be affected by overvoltage and overcurrent due to lightning strike, surge, and power line faults. Therefore, a protection design is required for subscriber ports of an access device. A general xDSL interface circuit is shown in FIG. 1. On the xDSL circuit, a transformer and a high-voltage capacitor are available for the bandwidth part, isolation and protection can be almost implemented. The major problem is about protection of a splitter. In an actual application, generally, a DSL device is installed in an outdoor cabinet, a plain old telephone service (Plain Old Telephone Service, shorted as POTS hereinafter) wire is connected to a central equipment room, and a Line (port of mixed DSL signal and POTS signal) wire is connected to a DSL subscriber's home, as shown in FIG. 2. As the POTS wire and the Line wire are connected to different places, the following situation may occur: A two-wire short-circuit fault or grounding fault occurs on one end and lightning strike, power line induction, or contact occurs on the other end; at this time, overvoltage is added to two ends of the splitter or high current passes the splitter, and in this case, the splitter is damaged.
A splitter of a DSL access device in the prior art is completely isolated and protected and no protection component is added to the splitter. For example, as shown in FIG. 3, the splitter includes: discrete inductance (L1, L2, L3) and capacitance component (C1, C2, C3, C4, C5), and the splitter uses a L3 inductance for filtering, in which the inductance L3 is used to suppress EMI (Election Magnetic Interference, election magnetic interference) common-mode induction. Ports of the splitter are completely isolated and protected. When P-XT or P-XR of the POTS at one end is short-circuited or to-ground short-circuited, horizontal surge voltage from the Line at the other end may be added to two ends of the splitter or high current passes the coil of the splitter due to contact, causing damage or on-fire to the splitter; reversely, when L-XT or L-XR of the Line at the other end is short-circuited or to-ground short-circuited, vertical surge voltage from the Line at the other end is added to two ends of the splitter or high current passes the coil of the splitter due to contact, also causing damage or on-fire to the splitter. In addition, the splitter as a discrete component has a large size, affecting density of a board.
POTS and Line ports of some xDSL devices in the prior art use the protection solution of the fuse (Fuse) plus the voltage-switch thyristor surge suppressor diode (Thyristor Surge Suppressor, shorted as TSS hereinafter), and the protection circuit is shown in FIG. 4. When T and R at one end of the circuit are short-circuit or to-ground short-circuited, as the loop resistance of the splitter is only about 20Ω, when the current passing the splitter is not high enough to reach the start voltage of the TSS, the TSS does not work and cannot protect the splitter. When horizontal or vertical power line from the other end contacts the current to pass the coil of the splitter, high current passes the splitter because even if the fuse exists, the maximum non-operating current of the fuse within 15 minutes is still high, for example, about 2 A, and the loop resistance of the splitter is about 20Ω, and the splitter is overheated after a long time and damage or fire results.
In the process of implementing the technical solutions of the present application, the splitter in the prior art has at least the following problem: The splitter is prone to be damaged when a two-wire short-circuit fault or grounding fault occurs on one end and lightning strike, power line induction, or contact occurs on the other end.